A serological comparison of pollen proteins from ‘Clementine tangerine’ versus those of 5 other morphologically similar Citrus cultivars was made to measure the degree of genetic relationships with ‘Clementine’. Among the tested Citrus cultivars the most related to ‘Clementine’ were ‘Baladi mandarin’ and ‘Baladi blood orange’. whereas ‘Sour orange’ and ‘Satsuma mandarin’ were least related. These findings support previous observations based on morphological characteristics, that the possible seed parent to ‘Clementine’ was ‘Baladi mandarin’. The serological evidence also indicates that ‘Baladi blood orange’ could be the pollen parent.